The subject matter herein relates generally to flexible circuits, and more particularly, to a system and method for controlling impedance in a flexible circuit.
Some electrical systems, such as servers, routers, and data storage systems, utilize connector assemblies for transmitting signals and/or power through the electrical system. Such connector assemblies typically include a backplane or a midplane circuit board, a motherboard, and a plurality of daughter cards. The connector assemblies also include one or more electrical connectors that are attached to the circuit board for interconnecting the daughter cards to the circuit board when the daughter card is inserted into the electrical system. A flexible circuit is electrically coupled to the daughter cards and the circuit board to transfer power and data signals therebetween. The flexible circuit includes a flexible substrate and at least one conductive pathway extending through the substrate. Generally. the conductive pathway is formed from thin copper. The flexible circuit includes connector pads that couple the conductive pathways to contacts on a midplane circuit board, a motherboard, and/or a daughter card. The connector pads are in electrical contact with the conductive pathway to form an electrical transmission path through the flexible circuit.
However, the connector pads and the conductive pathway may experience crosstalk. In particular. the conductive pathway generates electromagnetic fields that radiate outward from the conductive pathway. If the connector pads are positioned too close to the conductive pathway, an impedance of the connector pad may be reduced. Low impedance in the connector pad subjects the connector pad to interference from the electromagnetic fields generated by the conductive pathway. When the conductive pathway is operating at a high data rate that generates stronger electromagnetic fields, it becomes difficult to maintain consistent impedance through the connector pads. To improve the impedance of the connector pads, the connector pads are generally separated from the conductive pathway with cured dielectric materials. The electromagnetic field is weaker at locations further from the conductive pathway. The dielectric material separates the connector pads and the conductive pathway to position the connector pad in a location where the electromagnetic field is weaker.
However, cured dielectrics are typically either very thin and/or very expensive. A thin dielectric may not separate the connector pad and the conductive pathway a sufficient distance to properly maintain the impedance of the connector pad. The cost of the uncured dielectric is also proportional to a thickness of the dielectric. Accordingly, thicker uncured dielectrics are generally more expensive. As such, providing sufficient separation between the connector pad and the conductive pathway may not be cost effective.
Accordingly, there is a need for a low cost solution to maintain the impedance of a connector pad in flexible circuit.